1. Field of the Invention
The present invention relates to a high-voltage multilayer capacitor suitable for use in which a high voltage such as, for example, AC 250 V or DC 500 V, is applied, and particularly to a high-voltage multilayer capacitor in which a ceramic sintered compact and an internal electrode are modified for improving voltage resistance and preventing undesirable flashover.
2. Description of the Related Art
A capacitor used in applications in which a high voltage is applied is strongly demanded to have high voltage resistance, and suppress flashover in the outer surfaces thereof.
Therefore, as a multilayer capacitor which withstands a high voltage, capacitors having various structures have previously been proposed (for example, Japanese Unexamined Utility Model Publication Nos. 60-76028, 62-120333 and 58-56431, and Japanese Unexamined Patent Publication No. 62-210612).
FIGS. 3 and 4 are a sectional front view and a sectional plan view, respectively, illustrating an example of conventional high-voltage multilayer capacitors.
Referring FIGS. 3 and 4, a multilayer capacitor 31 comprises a ceramic sintered compact 32 composed of dielectric ceramics. The ceramic sintered compact 32 has a first external electrode 33 formed on the end surface 32a, and a second external electrode 34 formed on the end surface 32b. Although a capacity can be taken out through the first and second external electrodes 33 and 34, a plurality of capacity takeout portions are provided in the ceramic sintered compact 32 so as to be connected in series in the direction from the first end surface 32a to the second end surface 32b.
Namely, first internal electrodes 35a to 35c are formed at different heights so as to be drawn out of the end surface 32a. Also second internal electrodes 36a, 36b and 36c are formed at different heights so as to be drawn out of the end surface 32b. In addition, unconnected internal electrodes 37a to 37c, 38a to 38c, and 39a to 39c are formed between the first and second internal electrodes 35a and 36a, between the second internal electrodes 35b and 36b, and between the first and second internal electrodes 35c and 36c, respectively.
For these internal electrodes, unconnected internal electrodes 40a to 40d, and 41a to 41d are formed to be overlapped with the adjacent internal electrodes through the ceramic layers in the thickness direction.
Therefore, in the above-described internal electrode structure, structures each comprising eight capacity takeout portions, which are connected in series in the direction from the end surface 32a to the end surface 32b, are connected in parallel between the first and second external electrodes 33 and 34.
Namely, the multilayer capacitor 31 has a structure in which eight capacity takeout portions are connected in series, as described above, so that the voltage resistance is improved.
On the other hand, Japanese Unexamined Patent Publication No. 62-210612 discloses a multilayer capacitor having a structure in which ceramic layers having a relatively low dielectric constant are arranged above and below capacity takeout portions comprising internal electrodes, thereby suppressing flashover in the upper and lower sides of a sintered compact.
However, in the above-mentioned multilayer capacitor 31, the plurality of capacity takeout portions are arranged in series between the first and second external electrodes 33 and 34 to increase voltage resistance, but flashover in the surfaces of the ceramic sintered compact 32 cannot be prevented.
On the other hand, in the multilayer capacitor disclosed in Japanese Unexamined Patent Publication No. 62-210612, the layers having a relatively low dielectric constant are arranged on the upper and lower sides of the portion comprising internal electrodes to suppress flashover in the upper and lower sides of the ceramic sintered compact, as described above, but flashover in the side of the ceramic sintered compact cannot be effectively suppressed. In addition, since the layers having a low dielectric constant are simply provided, voltage resistance cannot be improved.